Fluorinated Elastomeric Protective Layers with Controlled Solvophobic Properties for Lithium Metal Batteries

The interfacial instability and dendritic growth of lithium (Li) remain key obstacles to the implementation of Li metal batteries (LMBs). Herein, we present in situ-formed polymer protective layers (PPLs) on Li to enhance interfacial stability and electrochemical performance. The PPLs comprise a fluorinated elastomer and Li6.4La3Zr1.4Ta0.6O12 fillers to tune mechanical integrity and ionic conductivity. While in situ photopolymerization enables conformal coating on Li, the fluorinated monomers are tailored to optimize solvophobicity for carbonate electrolytes. Among them, hexafluorobutyl acrylate-based PPL (H-PPL) exhibits optimal solvophobicity with an ionic conductivity of 0.20 mS cm–1, stretchability of 300%, and an adhesion strength of 5.1 N m–1, which suppresses electrolyte penetration and promotes uniform Li deposition. Consequently, full cells employing H-PPL-coated Li and LiNi0.8Co0.1Mn0.1O2 cathodes retain 87.8% capacity after 250 cycles at 1C, outperforming bare Li (67.6%). This study demonstrates that PPL with controlled solvophobicity leads to improved electrochemical performance of LMBs.